Membrane Electrode Assembly Testing Research Articles

Unveiling the role of catalytically active MXene supports in enhancing the performance and durability of cobalt oxygen evolution reaction catalysts for anion exchange membrane water electrolyzers

The role of 2D transition metal carbides, also known as MXenes, as active catalyst supports in Co-based oxygen evolution reaction (OER) catalysts was elucidated through a combination of experimental and computation electrochemistry. Through facile seeding of commericial Co nanoparticles on three different MXene supports (Ti3C2Tx, Mo2Ti2C3Tx, Mo2CTx), Co@MXene catalysts were prepared and their electrochemical properties examined for alkaline OER electrocatalysts. The OER activity enhancement of Co was significantly improved for Mo2CTx and Mo2Ti2C3Tx supports, but marginal on the Ti3C2Tx in rotating disk electrode and membrane electrode assembly tests. The Co@Mo2CTx exhibited the highest anion exchange water electrolysis performance of 2.11 A cm−2 at 1.8 V with over 700 h of stable performance, exceeding previous benchmarks for non-platinum group (non-PGM) metal OER catalysts. The superior performance was attributed to the strong chemical interaction of Co nanoparticle with the Mo2CTx MXene support. Insights into the electrochemical and chemical oxidation according to MXene type as related to cell durability, as well the effect of electrical conductivity and inherent boosting of electrocatalytic activity of Mo-based MXenes elucidated through density functional theory (DFT) calculations helped explain the performance and durability enhancement of Mo-based MXene supports over Ti3C2Tx supports.

Using a pressurized GDE setup to analyze effects of temperature and relative humidity on CO-stripping measurements on a commercial Pt/C ORR catalyst

This study successfully showcases the capabilities of a newly developed pressurized gas diffusion electrode (GDE) setup by conducting cyclic voltammetry and CO stripping measurements at temperatures up to 120 °C, while considering various relative humidity (RH) levels. Our results clearly demonstrate the feasibility of investigating the effects of RH and elevated temperatures above 100 °C using the pressurized GDE setup. In particular, a negative shift in the CO oxidation peak potential upon increasing temperatures is observed, whereas a reduction in RH leads to a positive potential shift of the CO oxidation peak as well as peak broadening. Additionally, our results highlight the heightened sensitivity of the Hupd peak to changes in temperature and RH, resulting in an underestimation of the electrochemically active surface area (ECSA). An essential aspect of this research is the successful replication of trends observed in membrane electrode assembly (MEA) measurements, providing strong validation for the reliability and effectiveness of our pressurized GDE approach as a valuable bridging tool toward MEA testing at elevated temperatures.

A Porous Wrinkled Graphitic Carbon as Corrosion‐Resistant Carbon Support for Durable Fuel‐Cell Catalysts

AbstractThe lifespan of proton‐exchange membrane fuel cells heavily relies on the durability of the carbon support of cathode catalysts. However, commercial carbon supports like ketjenblack (KB) and Vulcan carbon (VC) face the challenge of balancing porosity, surface area, and electrochemical stability. To address this issue, a 3D porous wrinkled graphitic carbon (PWGC) is designed and synthesized using a catalyst‐free, plasma‐enhanced chemical vapor deposition approach. The resulting PWGC possesses a hierarchically porous structure with a high surface area, a high degree of graphitization, and exceptional corrosion resistance. As a result, the Pt/PWGC catalysts with the use of PWGC as the carbon support demonstrate superior high potential stability compared to those made with KB and VC as the carbon support. Additionally, a sacrificial layer strategy is introduced to further reduce PWGC corrosion, resulting in Pt@C/PWGC catalysts that show significantly improved durability in membrane electrode assembly tests. After 5K voltage cycles from 1.0 to 1.5 V, the retention of electrochemically active surface area approaches 56.8%, surpassing the 23.6% retention of commercial Pt/C catalysts tested under the same conditions.

Electrochemically induced dilute gold-in-nickel nanoalloy as a highly robust electrocatalyst for alkaline hydrogen oxidation reaction

Ni-based nanomaterials are currently the most promising electrocatalysts for the alkaline hydrogen oxidation reaction (HOR), yet limited by their poor electrochemical stability. Herein, we report a nickel-gold nanodimer (Ni100Au1/C-P) synthesized via a galvanic replacement reaction, which via an electrochemical activation mostly transforms into highly dilute gold-in-nickel host nanoalloys (Ni100Au1/C-EA). The Ni100Au1/C-EA exhibits both a remarkable specific HOR activity of 47.3 µA cm-2Ni, 20% higher than Ni100Au1/C-P and 34% higher than Ni/C, as well as exceptional stability for 6000 cycles and CO-tolerance. Membrane electrode assembly tests further identify the practical application of Ni100Au1/C-EA, which delivers a power density of 192 mW cm−2 and good durability. Theoretical studies suggest that the formation of NiAu alloys is thermodynamically favored with the help of adsorbed hydrogen intermediates. The in situ-formed NiAu nanoalloy, with a lower d band center than Ni, is endowed with improved anti-oxidation ability and appropriate intermediate binding energy, leading to a robust and excellent HOR performance. This electrochemical activation route provides a straightforward and novel strategy for regulating the microstructure of materials and therefore the catalytic activity and endurance of catalysts.

Rationally Designed PGM-Free Catalyst MEA with Extraordinary Performance

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). However, the high cost of PGM catalysts is the major huddler for the widespread applications of fuel cell electric vehicles. To remove this cost obstacle of fuel cell commercialization, PGM-free catalysts have been considered as the replacement of PGM catalysts for ORR because of the low cost and relatively comparable performance with PGM catalyst. Fe-C-N complex is the one of the most active centers in PGM-Free catalyst groups. This type of catalyst shows excellent activity characterized using the rotation disk electrode (RDE), i.e., the half wave potential (E1/2 ) could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts cannot achieve the comparable performance to PGM catalyst. Since there are so many differences between PGM-free, and PGM catalysts e.g., activity, stability, surface conditions, particle size etc. The fabrication of PGM-Free catalyst MEA cannot simply borrow the methods from that of making PGM MEA. In addition, the thicknesses of catalyst layers of PFM-free are significantly thicker than that of PGM, i.e., 10 times. Hereby, we proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Such method pushes PGM-free MEA first ever achieved the current density of 50.8 mA cm-2 at 0.9 V iR-free in H2/O2 and over 150 mA cm-2 at 0.8 V in H2/air, which surpassed the 2025 performance targets of US Department of Energy (DOE) for PGM-Free catalyst MEA. Further, the property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using mercury intrusion porosimetry (MIP), MEA testing. A property-structure-performance relationship has been established.

Oxygen reduction reaction measurements on platinum electrocatalysts in gas diffusion electrode half-cells: Influence of electrode preparation, measurement protocols and common pitfalls

Recently, half-cell gas diffusion electrode (GDE) setups have been presented as a powerful tool and promising alternative to rotating-disk electrode (RDE) as also membrane electrode assembly (MEA) testing of oxygen reduction reaction (ORR) catalysts. While RDE testing aims to extract isolated kinetic data, GDE testing allows characterization of realistic fuel cell catalyst layers at application relevant current densities and potentials, where also phenomena besides catalyst kinetics play a role. Nevertheless, while for RDE as also MEA testing dedicated protocols for reliable electrode preparation and assessment of activity were developed, and are backdrop for trustworthy and comparable data, these are missing for the novel half-cell GDE testing. This work identified key challenges in running and evaluation of half-cell GDE measurements, which are e.g. ink composition and electrode preparation, falsification of electrochemical active surface area using hydrogen uptake measurements, influence of joule heating at high current densities and importance of solution resistance correction. A commercial half-cell GDE, as well as a commercial catalyst, were employed, allowing fast application of the developed protocols, while the general findings can also be translated to other GDE setups.

The gas diffusion electrode setup as a testing platform for evaluating fuel cell catalysts: A comparative RDE‐GDE study

AbstractGas diffusion electrode (GDE) setups have been recently introduced as a new experimental approach to test the performance of fuel cell catalysts under high mass transport conditions, while maintaining the simplicity of rotating disk electrode (RDE) setups. In contrast to experimental RDE protocols, for investigations using GDE setups only few systematic studies have been performed. In literature, different GDE arrangements were demonstrated, for example, with and without an incorporated proton exchange membrane. Herein, we chose a membrane‐GDE approach for a comparative RDE–GDE study, where we investigate several commercial standard Pt/C fuel cell catalysts with respect to the oxygen reduction reaction (ORR). Our results demonstrate both the challenges and the strengths of the new fuel cell catalyst testing platform. We highlight the analysis and the optimization of catalyst film parameters. That is, instead of focusing on the intrinsic catalyst ORR activities that are typically derived in RDE investigations, we focus on parameters, such as the catalyst ink recipe, which can be optimized for an individual catalyst in a much simpler manner as compared to the elaborative membrane electrode assembly (MEA) testing. In particular, it is demonstrated that ∼50% improvement in ORR performance can be reached for a particular Pt/C catalyst by changing the Nafion content in the catalyst layer. The study therefore stresses the feasibility of the GDE approach used as an intermediate “testing step” between RDE and MEA tests when developing new fuel cell catalysts.

Effects of Ink Formulation on the Structure and Performance of PGM-Free Catalyst Layer in PEMFCs

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). However, the cost of PGM catalysts is very high. Particular, the cost becomes unaffordable if the PEMFC is in massive application. In order to remove this cost obstacle of fuel cell commercialization, PGM-free catalysts have been considered as the replacement of PGM catalysts for ORR because of the low cost and the reasonable performance. Fe-C-N complex is the one of the most active centers in PGM-Free catalyst groups. This type of catalyst shows very promising activity in rotation disk electrode (RDE) testing. The half wave potential could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts is not good enough to replace the PGM catalysts. Since the PGM-free catalysts are so different from the PGM catalysts in terms of catalytic activity, stability, surface conditions, particle size etc, the fabrication of PGM-Free catalyst MEA cannot simply copy the method of making PGM MEA. In addition, the thicknesses of catalyst layers of PFM-free are significantly thicker than that of PGM, for example, 10 times. We proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Using this method, the PGM-free catalyst MEA achieved the current density 44.9 mA cm-2 at 0.9 ViR-free in H2/O2 and 150 mA cm-2 at 0.8 V in H2/air, which surpassed the performance targets of US Department of Energy (DOE) for PGM-Free catalyst MEA. The property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using ultra-small angle x-ray scattering (USAXS), cyro-TEM, mercury intrusion porosimetry (MIP), SEM/EDAX, RDE and MEA testing. A property-structure-performance relationship has been established.

Effects of Ink Formulation on the Structure and Performance of PGM-Free Catalyst Layer in PEMFCs

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). The cost becomes unaffordable if the PEMFC is in massive application. The PGM-Free catalyst shows very promising activity in rotation disk electrode (RDE) testing. The half-wave potential could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts is not good enough to replace the PGM catalysts. Since the PGM-free catalysts are so different from the PGM catalysts in terms of catalytic activity, stability, surface conditions, particle size, etc., the fabrication of PGM-Free catalyst MEA cannot simply copy the method of making PGM MEA. We proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Using this method, the PGM-free catalyst MEA achieved the current density 44.9 mA cm-2 at 0.9 V iR-free in H2/O2 and 150 mA cm-2 at 0.8 V in H2/air, which surpassed the performance targets of US Department of Energy (DOE)for PGM-Free catalyst MEA. The property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using, mercury intrusion porosimetry (MIP), MEA testing. A property-structure-performance relationship has been established.

Influence of PtCu/C Catalysts Composition on Electrochemical Characteristics of Polymer Electrolyte Fuel Cell and Properties of Proton Exchange Membrane

The present work aimed to investigate the influence of “weakly bound“ copper dissolution from the surface of bimetallic PtCux/C catalysts on the properties of proton exchange membrane and the membrane electrode assembly (MEA) in general. A number of PtCux/C materials have been obtained by the simultaneous reduction in copper and platinum precursors in the course of liquid-phase synthesis with a varying ratio of metals from PtCu2.0/C to PtCu0.3/C. All bimetallic PtCux/C electrocatalysts after the activation stage exhibit high activity in the oxygen electroreduction reaction. The PtCux/C catalysts in “as prepared” state were tested in MEA. The increase in Cu content in PtCux/C catalysts led to a decrease in current density of MEA while its resistance was almost independent of the Cu fraction in the catalyst. The membrane saturation degree by Cu2+-ions after MEA testing did not exceed 40%, even in the case of the PtCu2.0/C material. The main reason for the degradation of membrane electrode assembly with PtCux/C materials is the transport limitation caused by the contamination of Nafion in three catalytic layer by “weakly bound” copper ions.

Enhanced Catalyst Stability Via Chemically Grafted Polyaniline Groups for PEMFC

The promising performance from the platinum group metal (PGM) catalysts make them the most practical catalysts for the commercialization of the polymer membrane fuel cells (PEMFCs). However, the excellent initial performance is not good enough for massive applications, particular for the fuel cell vehicles, which requires the long-term durability. Both the performance and the durability of catalysts strongly impact the applications in a wide range of operations of fuel cells, from stationary power generation to the transportation power propulsion. Catalyst stability plays a very important role on reducing the operation cost and increasing the lifetime of PEMFCs. Herein, a concept is proposed, which enhances the lifetime of PEMFCs through engineering the surface of catalyst supports. By covalently grafting NH2 groups on carbon (NGCB) surface, followed by polymerizing polyaniline (PANI) onsite on NFCB surface (using introduced NH2 groups as precursor), Pt L-edge goes to higher energy level, suggested by XAS measurement. Such modification can increase the barrier for Pt’s oxidation. In this study, carbon supports with different PANI loadings were synthesized and the Pt nanoparticles were loaded onto these supports. The synthesized catalysts were characterized for their morphology and structure using TEM, XRD, BET and Hg porosimetry. Both RDE and MEA tests were carried out for these catalysts for their fuel cell performance. The results show that the energy levels of Pt L-edge were increased with PANI loading. Besides, the membrane electrode assembly (MEA) testing results prove that the catalyst stability was improved with PANI loading in certain range. Three different PANI loadings were analyzed: 0.2, 0.25 and 0.33 in mass fraction of NFCB. MEAs results show that the beginning of life (BOL) performances of three catalysts were almost same. But when it comes to the catalyst stability test, the performance losses between BOL and EOL at 0.8 A·cm-2 in air are 120 mV, 90 mV and 45 mV for the three catalysts, respectively, after 30k square wave cycling using the standard testing protocol from the Department of Energy (DOE).

Recent developments in Pt–Co catalysts for proton-exchange membrane fuel cells

Development of Pt-based oxygen reduction reaction catalysts with high efficiency and high durability is central to the application of proton-exchange membrane fuel cell systems. Pt–Co bimetallic catalysts have drawn extensive attention owing to their capability of delivering high performance and long lifetime for fuel cell applications including light-duty and heavy-duty vehicles. However, further improvements in durability and performance are needed to meet market requirements. To fully exploit the potential of Pt–Co catalysts, new insights into the relationship between catalyst properties and fuel cell performance and durability are needed, and more effective methods to tailor the features of Pt–Co catalysts need to be developed. This review provides a summary and perspective on recent efforts, including work on customizing the Pt shell and Pt:Co ratio, tailoring the crystal structure, and improving carbon support properties, with a particular emphasis on mechanisms leading to enhancement of mass activity, power density, and durability in membrane electrode assembly testing.

Molecular Design of Single‐Atom Catalysts for Oxygen Reduction Reaction

AbstractFuel cells are highly attractive for direct chemical‐to‐electrical energy conversion and represent the ultimate mobile power supply solution. However, presently, fuel cells are limited by the sluggish kinetics of the cathodic oxygen reduction reaction (ORR), which requires the use of Pt as a catalyst, thus significantly increasing the overall cost of the cells. Recently, nonprecious metal single‐atom catalysts (SACs) with high ORR activity under both acidic and alkaline conditions have been recognized as promising cost‐effective alternatives to replace Pt in fuel cells. Considerable efforts have been devoted to further improving the ORR activity of SACs, including tailoring the coordination structure of the metal centers, enriching the concentration of the metal centers, and engineering the electronic structure and porosity of the substrate. Herein, a brief introduction to fuel cells and fundamentals of the ORR parameters of SACs and the origin of their high activity is provided, followed by a detailed review of the recently developed strategies used to optimize the ORR activity of SACs in both rotating disk electrode and membrane electrode assembly tests. Remarks and perspectives on the remaining challenges and future directions of SACs for the development of commercial fuel cells are also presented.

Performance Test of Membrane Electrode Assembly in DAFC using Mixed Methanol and Ethanol Fuel with Various Volume Comparison

Direct Alcohol Fuel Cell (DAFC) performance is influenced by electrocatalysis reactions that occur in Membrane Electrode Assembly (MEA). In this study, MEA was made with Pt-Ru/C (anode) and Pt/C (cathode) catalysts. The results of the electrode characterization with XRD showed a carbon peak at 26.63° and Ru at 40.58°. Based on the results of Cyclic Voltammetry (CV) measurements, the Electrochemical Surface Area (ECSA) electrode value is known to be 373.601 cm2/mg. Meanwhile, the impedance value is 4.315 Ω and the electrical conductivity value is 6.61x10-4 S/cm. MEA testing using MeOH 3 M fuel produces Open Circuit Voltage (OCV) of 0.650 V. Meanwhile, MEA performance testing uses a mixture of methanol and ethanol 2 M in loading conditions obtained the best mixture of fuel composition is methanol: ethanol = 90:10 with a maximum power density of 4.34 mW/cm2 and is able to maintain the voltage at 0.649 V under conditions of 6.875 mA/cm2. The results also showed that the volume of ethanol which was too high resulted in a decrease in cell performance in the fuel mixture caused by the competition of adsorption between competing methanol and ethanol occupying the active site of the catalyst. Keywords: DAFC, fuel cell, Pt-Ru/C, ethanol, methanol, Open Circuit Voltage

Development of a Common Differential Fuel Cell Test Fixture and Protocols to Expedite Material Development

Many test fixtures used for Membrane Electrode Assembly (MEA) development by the fuel cell community have major design drawbacks that both reduce the confidence in data sets and make the sharing of results difficult. A new common hardware design that incorporates the learnings and best practices from various technical leaders is needed to improve build robustness and reduce cell-to-cell variation. Such common hardware can yield improved data quality and accurate comparisons, thus accelerating materials development. Further, creating a common set of differential cell protocols along with corresponding data processing tools can facilitate sharing of results and researcher confidence in data quality. The design objective of the single cell hardware is to ensure MEAs are exposed to uniform conditions during testing of both performance and durability with minimal influence due to the flow field. In this talk, we will present the design and results from a simplified test hardware that can improve the overall quality of testing and facilitate comparisons from lab-to-lab. The design ensures as much as possible a uniform distribution of all physical quantities such as velocity, pressure, temperature, and oxygen concentration in the flow field. Minimal oxygen concentration gradient across land-channel is ensured in the design with parallel flow fields, having fine land of 0.24 cm, and operating at high (>10) stoichiometry. Pressure drop across the inlet and outlet ports in the hardware is also reduced by designing the ports for minimal restriction. Temperature and compression uniformity is also ensured in the design. The hardware is set to operate with stress control through a pneumatic system integrated into the anode end-plate with the additional capability to regulate compression during operation. To investigate the uniformity of key paramaters, FEA, CFD, thermal, and ohmic analyses were performed on the designed cell. Hardware replicates will be tested at multiple labs, and an operating procedure will be developed and shared with the community. Assuming successful development, we propose broad adoption of this hardware across the community as a common MEA testing platform. Figure 1

Platinum Group Metal-Free Direct Hydrazine Alkaline Membrane Fuel Cells for Automotive Applications

Over the last decade, research team from Daihatsu Motor Co. has introduced the concept of anion-exchange membrane fuel cell with liquid fuels for automotive applications. Switching from more commonly used proton exchange membranes (PEM) to alkaline, anion-exchange membranes (AEM) has several kinetic and materials benefits and opens the possibility of developing Fuel Cell Vehicle (FCV) entirely based on Platinum Group Metal-free (PGM-free) technology.1 This has been made possible by the adoption of hydrazine hydrate as a liquid fuel, which affords technology deployment while using the existing fuel distribution and dispensing technology. This concept pioneered the use of AEM Fuel Cells for automotive applications worldwide and created the state of the art AEM Fuel Cell stack technology2. UNM team has been a long-term participant in the multi-institutional program led by Daihatsu Motor Co., focusing on the development of Oxygen Reduction Reaction (ORR) catalysts and selective hydrazine electro-oxidation catalysts used as cathode and anode material in AEM membrane electrode assembly (MEA)3. The theoretical electromotive force of such direct hydrazine fuel cell is 1.56V and hydrazine hydrate as a fuel can be oxidized by number of catalysts using exclusively Earth-abundant metals, such as NiZn unsupported catalysts developed at UNM4. This line of research has been continued in NiLa5 and supported Ni-allowed catalysts6 aiming not only high activity, but also extreme selectivity of hydrazine electro-oxidation to N2 and H2O only. Elucidating the mechanism of hydrazine oxidation included EXAFS/XANES study7 and let to formulating of the hypothesis of the reaction mechanism8 that involves surface hydroxyl groups on Ni as critical participants in the hydrazine dehydrogenation reaction step (see Fig. 1). The role of the nickel, secondary metal phase and the carbon support in the activity and durability of Ni-allow catalysts will be discussed. ORR catalysts developed under this program included initially Co-polypyrrole materials system9. The mechanism of oxygen reduction and the structure-to-property relationships have been described in a recent EXAFS/XANES study10. This paper will present a family of Fe-Nitrogen-Carbon ORR catalysts that were used in the successful stack development and Daihatsu FCV prototype tests. This new generation Fe-containing PGM-free catalysts are synthesized by UNM Sacrificial Support Method (SSM) a type of for templated synthesis of hierarchically structured electrocatalysts materials.11-13 In this method the catalysts precursors are being absorbed on, impregnated within or mechanically mixed with the support (usually mono-dispersed or meso-structured structured silica), thermally processed (pyrolyzed) and then the silica support is removed by etching (in KOH or HF) to live the open frame structure of a “self-supported” material that consists of the catalysts only. Such hierarchical structures are advantageous in enhancement of the fuel cell performance since they correspond to the different levels of transport in the corrugated electrode matrixes. A wide variety of materials can be made by these methods in which not only the composition but also the microstructure can be varied. It is the combination of these attributes - control over microstructure at a number of different length scales and composition, simultaneously - that is extremely important to the performance of the electrocatalyst materials in a fuel cells. The high activity of these Fe-N-C cathode catalysts was confirmed in both RDE and MEA tests. As synthesized materials were extensively studied by XPS, SEM, TEM, BET and other methods, in order to elucidate the structure-to-properties correlations. This paper describes a new class of templated, self-supported PGM-free catalysts derived by sacrificial support method (SSM) and their activity in free alkaline electrolyte (KOH) and in anion-exchange MEA. P. Atanassov and A. Serov, Japanese Society of Automotive Engineers, 67 (2013) 68-71J. Varcoe, P. Atanassov, et al., Energy & Environmental Science, 7 (2014) 3135-3191A. Serov, M. Padilla, et al., Angewandte Chemie Intern. Ed., 53 (2014) 10336 –10339U. Martinez, K. Asazawa, et al., Physical Chemistry & Chemical Physics, 14 (2012) 5512-5517T. Sakamoto, K. Asazawa, et al., J. Power Sources, 234 (2013) 252-259T. Sakamoto, K. Asazawa, et al., J. Power Sources, 247 (2014) 605-611T. Sakamoto, D. Matsumura, et al., Electrochimica Acta, 163 (2015) 116-122T. Sakamoto, H. Kishi, et al., Electrochimica Acta, (2016) in pressT.S. Olson, S. Pylypenko, et al., J. Phys. Chem. C., 114 (2010) 5049–5059K. Asazawa, H. Kishi, et al., Journal of Physical Chemistry - C, 118 (2014) 25480–25486S. Pylypenko et al., Electrochimica Acta, 53 (2008) 7875-7883A. Serov et al., Electrochem. Comm., 22 (2012) 53-56Serov et al., Advanced Energy Materials, 4 (2014) DOI: 10.1002/aenm.201301735Serov, et al., Nano Energy, 16 (2015) 293-300 Figure 1

Cathode Catalyst Layer Design and Optimization for Portable Power Applications Using Non-Precious Metal Catalysts

In recent years, the inherent activity of M/N/C (M=Fe, Co, or Mn) non precious metal catalyst (NPMCs) has advanced to a stage where these catalysts can be considered as potential alternatives to Pt/Pt-alloy catalysts for certain applications(1-4), provided stability/durability can be improved(5). Due to these achievements, NPMCs have advanced beyond purely rotating disc electrode (RDE) studies, and are now ready to be thoroughly evaluated at the membrane electrode assembly (MEA) level. While previous work has looked at in-situ MEA evaluation of NPMCs, few of these studies have investigated maximizing performance through rational design of the cathode catalyst layer (CCL). However, recent work by Serov et al. (3) has highlighted the importance of CCL design parameters in maximizing the performance of NPMC-based CCLs. The significant difference in CCL layer thickness of NPMC-based CCLs vs. conventional Pt/C CCLs means any optimization used for conventional Pt/C CCLs will likely not apply to these novel NPMC CCLs. This provides the research community with significant opportunity in this largely unexplored area. In this work, we will present some of our recent findings on designing and optimizing NPMC-based CCLs for portable power and backup power applications. The NPMC used in this work is developed by Nisshinbo Holdings, and has demonstrated world-leading performance in laboratory scale (50 cm2) MEA testing. After a brief discussion on the synthesis of this NPMC, the results of optimizing the CCL design (e.g. ionomer type/content) will be shown. Performance data recently obtained under conditions relevant for portable power/backup power will be presented and compared against product requirements. Acknowledgements The authors thank Alan Young for many helpful discussions,

Electrochemical MEA Characterization: Area Specific Resistance Corrected to Fuel Utilization as Universal Characteristic for Cell Performance

Membrane-electrode-assembly (MEA) is a heart component of SOFC and defines the limits for power density, efficiency and durability available for exploitation in stacks and systems. MEA performance is often given as measure for possibilities of fuel cell technology. Most widespread way to communicate the MEA performance is to present the I-U-characteristic at a constant temperature and to estimate the area specific resistance from the slope of this curve. Other methods for characterization of performance like current density, impedance and local resistance measurement under defined operating conditions also have been used for this purpose. The fuel composition worldwide used for MEA tests (from dry hydrogen to H2:H2O=50:50) is connected with open circuit voltage which has great impact on measured performance. Moreover the realized fuel utilization strongly depends on operating conditions and varies in broad range. For these reasons it is difficult to compare results achieved by different researchers. It is beneficial to define unified value which would characterise electrochemical MEA performance. To resolve this challenge the voltage drop during the cell performance have been mathematically separated in two parts: (i) voltage drop due to change of Nernst voltage as a result of fuel utilization (and humidification) by current flow and (ii) voltage drop due to ohmic and polarization losses in the cell. This approach allows to separate the influence of non-linearity of Nernst voltage dependence from current on estimated cell resistance. It was found that at temperatures above 750°C the area specific resistance of the cell corrected to the Nernst voltage drop (fuel utilization) is a constant value, which only weakly depend on fuel composition. Favourable operating conditions as well as influence of operating conditions for estimation of cell resistance will be presented.

Indium Tin Oxide as Catalyst Support for PEM Fuel Cell: RDE and MEA Performance

Introduction Conventional carbon supports suffer from catastrophic failure during start-up/shut-down events, which result in high cathode interfacial potentials, which, in turn, lead to carbon corrosion and catalyst degradation. Carbon corrosion is a major problem in fuel cells because it leads to loss of catalyst activity and collapse of electrode structure. Nissan, as an automotive OEM, has always approached the issue of catalyst support durability at the materials level, rather than at the systems-level, since system-level mitigation is an added cost to the balance of plant (BOP), and presents one additional factor that can fail during operation. NTCNA and IIT have been working on the development of high-surface-area, corrosion-resistant non-carbon supports, and we have previously demonstrated a class of highly stable non-carbon supports, e.g. ruthenium-titanium oxide (RTO) (1). In this work, we present the results of our work on a second class of non-carbon supports - tin-doped indium oxide (ITO). Materials and Methods RDE Testing – RDE tests were performed in a 3-compartment electrochemical cell containing 0.1 M HClO4 electrolyte. A glassy carbon disk (0.196 cm2) uniformly covered with Pt/C or Pt/ITO catalyst served as the working electrode. The counter and reference electrodes were Pt foil and RHE, respectively. Membrane Electrode Assembly (MEA) Fabrication - Catalyst inks were prepared by mixing Pt/C or Pt/ITO with water, n-propanol, and a Nafion ionomer dispersion. The mass-based ionomer/support (I/S) ratio in the ink was kept constant at 0.9. The cathode catalyst layers were formed on GDLs using an automated robotic spray system. MEAs (25 cm2) were prepared by hot pressing cathode GDEs (0.35 mgPt/cm2) and commercial anode GDEs (0.4 mgPt/cm2) onto Nafion® NR211 membranes. Results and Discussion Figure 1 shows the RDE performance of Pt/ITO vs. a commercially available Pt/C benchmark catalyst of comparable Pt particle size. The ECA obtained for Pt/ITO (22 m2/gPt) was lower than Pt/C (45 m2/gPt) due to the low surface area of ITO which causes Pt particle agglomeration. Even with a lower ECA, Pt/ITO shows promising performance since its mass activity of ~150 mA/mgPt matches that of the Pt/C benchmark catalyst. However, we have repeatedly observed that Pt/ITO performs very poorly in MEA testing. Figure 2 shows a typical H2/O2 polarization curve obtained for Pt/ITO at a high Pt loading of 0.35 mg/cm2. The only difference between the two MEAs is the cathode catalyst. Other than the dramatic difference between the two polarization curves, it can also be seen that Pt/ITO shows a very high HFR (high frequency resistance) of ~220 mΩ·cm2. The HFR represents the ohmic resistance due to proton transport in the membrane and the electronic contact resistances in the cell. The high HFR is attributed to the poor electronic conductivity of the ITO support since the two MEAs in Figure 2 have the same membrane, cell hardware, and cell components. It is hypothesized that hydroxylated species form on the ITO surface under fuel cell operating conditions. Hydroxide and oxy-hydroxide species may readily form on the surface of ITO due to hydrolysis reactions. Hydroxylated species such as In(OH)3 have low solubilities, hence they may remain adsorbed on the ITO surface, forming a passivating layer that will increase ohmic resistance (2). Furthermore, the Pourbaix diagram for indium shows that under fuel cell conditions, the formation of In3+ is favorable, and it is possible that In3+ can act as a poison that covers the Pt active sites. This is supported by the changes observed in the CV profile in MEA (loss of Hupd features and resistive behavior), suggesting some changes in the chemical properties of ITO and Pt poisoning. The promising RDE results did not translate to good performance in MEA, and this is hypothesized to be caused by cross-over hydrogen in MEA. H2 crossing over from anode to cathode may accelerate the formation of hydroxylated species. Experiments are underway to verify this.

Proton Conductivity and Gas Barrier Properties of Graphene Oxide for PEMFC Membranes

Treatment of graphite by the modified Hummers method results in exfoliation of the graphene layers and the introduction of oxygen-containing surface functional groups.1 The resulting graphene oxide offers interesting possibilities for a wide range of applications in areas as diverse as e.g. humidity sensing,2 molecular sieving,3 gas barriers,4 dielectrics,5 and fuel cells.6,7 Polymer electrolyte membrane fuel cells (PEMFCs) are seen as a sustainable energy source for the future. So far the most commonly used membrane in PEMFCs is Nafion, due to its high mechanical and chemical stability as well as its high proton conductivity. However Nafion is expensive, has limited performance at temperatures > 100°C,8 and has only moderate gas barrier properties (leading to fuel crossover in very thin membranes). Graphene oxide membrane fuel cells (GOMFCs) have displayed reasonable power densities at room temperature,7and with some improvements could act as an electrolyte in low temperature fuel cells. Here, the proton conductivity, fuel cell performance, fuel crossover of graphene oxide paper with different oxygen content, surface morphology, and surface functional groups are investigated by impedance spectroscopy, membrane electrode assembly testing, and gas permeation measurements. The manufacturing techniques for production of graphene oxide membranes and the optimal thickness of membranes are also discussed.